Fragrances are of great interest especially in the field of cosmetics and also laundry and cleaning detergents. Fragrances of natural origin are mostly expensive, often limited in their available amount and, on account of fluctuations in environmental conditions, are also subject to variations in their content, purity etc. To circumvent these undesirable factors, it is therefore of great interest, by way of example, to chemically modify readily available natural substances, e.g. readily available fragrances of natural origin, to create substances, which have organoleptic properties that resembles more expensive natural fragrances or which have novel and interesting organoleptic profiles. Such “semi-synthetic” substances can, by way of example, be used as substitutes for purely natural substances on account of their odor, where substitute and natural substance do not necessarily have to have a chemical-structural similarity.
Caryophyllene and its analogs are known fragrance chemicals. Caryophyllene is a natural product, which can readily be isolated from clove oil. Some of its oxidation products are also described in the state of the art.
There is a constant need for novel processes, e.g. by making use of mild oxidation reactions, to improve the production of aroma chemicals with advantageous sensory properties.
Starokon et al., Adv. Synth. Catal. 2004, Vol. 346, pp. 268-274, describe the oxidation of 1-methyl cyclohexene with N2O. 1-methyl cyclohexene was oxidized in substance at 250° C. under 25 bar of N2O for 12 hours. The conversion of 1-methyl-cyclohexene in this reaction was 33% and a product mixture containing 2-methylcyclohexanone as the main product (44% selectivity), methyl cyclopentyl ketone (34% selectivity), methyl-pent-4-en-1-yl-ketone (5% selectivity) and 5-heptenal (2-3% selectivity) was obtained.
Hermans et al., Phys. Chem. Chem. Phys., 2007, Vol. 9, pp. 4269-4274, describe a similar oxidation reaction of 1-methyl cyclohexene with N2O, which gave the same reaction products in almost identical selectivities. They also observed a very low reaction rate for this oxidation reaction.
Beta-caryophyllene ((1R,4E,9S)-4,11,11-trimethyl-8-methylene-bicyclo[7.2.0]undec-4-ene) and its analogs are known fragrance chemicals. Several of its oxidation products are also described in the state of the art.
Sköld et al., Food and Chemical Toxicology, 2006, Vol. 44, pp. 538-545, describe the air oxidation of the fragrance chemical beta-caryophyllene to caryophyllene oxide and its allergenic activity.
Collado et al., Nat. Prod. Reports, 1998, Vol. 15, pp. 187-204, describe the physical properties and reactivity of beta-caryophyllene in detail, including its oxidation products that are obtained from various oxidation reactions.
Matsubara et al., Nippon Nogei Kagaku Kaishi, 1985, Vol. 59, Nr. 1, pp. 19-24, and Uchida et al., Agric. Biol. Chem., 1989, Vol. 53, Issue 11, pp. 3011-3015, describe the oxidation of beta-caryophyllene with lead tetraacetate and the analytical characterization of the obtained oxidation products. Besides 11 other compounds, they identified 1-[(1R,4R,8S)-10,10-dimethyl-7-methylene-4-bicyclo[6.2.0]decanyl]ethanone and 1-[(1R,4S,8S)-10,10-dimethyl-7-methylene-4-bicyclo[6.2.0]decanyl]ethanone in the oxidation product mixture. Specifically, the oxidation reaction is performed by reacting beta-caryophyllene with lead(IV) acetate in stoichiometric quantities, upon which 1-[(1R,4R,8S)-10,10-dimethyl-7-methylene-4-bicyclo[6.2.0]decanyl]ethanone and 1-[(1R,4S,8S)-10,10-dimethyl-7-methylene-4-bicyclo[6.2.0]decanyl]ethanone were obtained in a selectivity of 10.2% and 9.9%, respectively. Furthermore, they propose the potential use of these oxidation products in perfumes, due to their mildly woody odor.